This invention relates to arrays of acoustic sensors that facilitate the non-invasive detection of coronary artery disease (CAD).
The 20186 application describes an invention for the non-invasive in vivo detection and localization of abnormal blood flow. Embodiments of that invention display the spatial distribution of phase coherence in the shear eave component of blood flow signals generated by an acoustic sensor array. An essentially uniform display indicates normal blood flow. A non-uniform display may indicate the presence of an occlusion and the presence or extent of abnormal, turbulent blood flow. Poor correlation of signals from the array sensors may adversely affect the display uniformity.
Acoustic sensor arrays are conventionally positioned above a measurement area defined as the hairless human chest skin located vertically between the sternum and a parallel line passing through the left nipple and horizontally 10 cm above and 6 cm below the left and right nipples.
A prior art acoustic sensor array comprising eight equally spaced sensors in two concentric circles having prime numbers of sensors in each circle and a ninth sensor at the common center of the concentric circle is illustrated by FIG. 6 of the 20186 application.
To reach sensors in a conventionally positioned prior art array as described in the 20186 application, sound waves must travel either directly through lung tissue or first to the body surface and then laterally with consequent attenuation of correlation. A study of the correlation by that array of patient data signals generated by the quiet interval revealed that only four or five of the nine sensors are well correlated.
It is known that a notch (xe2x80x9ccardiac notchxe2x80x9d) in the human left lung allows the heart to be in contact with the chest wall. Well correlated blood flow signals may be generated by acoustic sensors positioned on a human chest in a small area (xe2x80x9cacoustic windowxe2x80x9d) located above the cardiac notch. The bounds of the acoustic window have been approximated by ultrasonic probe means as described in this application and by locating the portions of sensor corresponding to channels achieve the highest apparent signal to noise ratio (SNR) as described in the Stearns application.
Acoustic Window
An area above the notch in the human left lung which allows the heart to be in contact with the chest wall. Well correlated acoustic blood flow signals of good quality may be generated by a sensor array positioned on a patient""s chest within or substantially within the perimeter of an acoustic window.
Sensor or Accelerometer
Any current or voltage mode device which generates an electric signal from displacement or a derivative thereof upon detection of a sound wave.
Sensor Array
A pattern or spaced arrangement of a plurality of sensors on or to be placed on the body surface of a patient.
Sensor Array Aperture
The space or area within the perimeter of an array.
Sensor Array Geometry
The shape of the perimeter of a sensor array.
Channel
The path to a receiver followed by a signal from the sensor by which the signal is generated.
Pursuant to one embodiment of the invention, an acoustic window may be defined by ultrasonic probe means. The invention includes sensor arrays having an aperture locatable within or substantially within the bounds of an acoustic window when the array is positioned on the chest of a person.
An important aspect of the invention includes the identification of an acoustic window comprising the merged acoustic window sub-areas corresponding to two or more intercostal spaces (ICS""s), and array designs to accommodate such acoustic windows.